This application is based on Japanese Application No. 2000-173971, filed Jun. 9, 2000, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates generally to a four-cycle engine, and more particularly to an improved cylinder head for a four-cycle engine.
2. Description of Related Art
Relatively small watercrafts such as, for example, personal watercrafts have become very popular in recent years. This type of watercraft is quite sporting in nature and carries one or more riders. A hull of the watercraft typically defines a rider""s area above an engine compartment. An internal combustion engine powers a jet propulsion unit that propels the watercraft by discharging water rearwardly. The engine lies within the engine compartment in front of a tunnel which is formed on an underside of the hull. At least part of the jet propulsion unit is placed within the tunnel and includes an impeller that is driven by the engine.
A four-cycle engine can be used in a personal watercraft. Typical four cycle engines include an exhaust system to discharge exhaust gases from one or more combustion chambers. The engine typically has a cylinder head member in which one or more inner exhaust passages are defined. Typically, one or more exhaust valves are provided to connect or disconnect the inner exhaust passages with the combustion chambers.
A valve actuation mechanism such as, for example, a combination of a camshaft with coil springs, can intermittently actuate the exhaust valves to bring them to an open position and a closed position. When each exhaust valve is in the open position, the associated inner exhaust passage is connected with the corresponding combustion chamber. When the valve is in the closed position, the exhaust passage is disconnected from the combustion chamber.
In some four cycle engines, each exhaust valve has a retainer opposite to a valve head and the coil spring urges the retainer to bring the valve head toward the closed position. The exhaust valve also has a valve lifter placed over the retainer and the camshaft pushes the valve lifter toward the open position. The cylinder head member defines guide openings through which the valve lifters can slide.
In some arrangements, one or more exhaust manifolds can depend from the cylinder head member. The exhaust manifolds define outer exhaust passages communicating with the respective inner exhaust passages to deliver the exhaust gases to a downstream portion of the exhaust system. The exhaust manifolds can be affixed to mount bosses formed on the cylinder head member by, for example, bolts.
One aspect of the present invention is a discovery that in engines which have exhaust manifolds affixed to mount bosses formed on the cylinder head member, the weight of the exhaust manifolds can deform the guide openings. For example, in some engines, the mount bosses are located adjacent to the guide openings of the valve lifters. It has been found that the weight of the exhaust manifolds deforms the guide openings. With sufficient deformation, movement of the valve lifters within the openings is adversely affected.
A need therefore exists for an improved four-cycle engine that can prevent a guide opening for an exhaust valve assembly from deforming by the weight of an exhaust manifold or conduit depending from a cylinder head member in which the guide opening is defined.
In some configurations of the exhaust manifold for the watercraft, a water jacket is formed through which water flows to cool the exhaust manifold. Another aspect of the invention includes the discovery that such water can be heavy enough to increase the deformation of the guide openings.
Another need thus exists for an improved four-cycle engine for a watercraft that can have an exhaust manifold that ensures a large capacity of a water jacket.
As described above, a four-cycle engine is provided with a valve actuation mechanism. Because the mechanism requires a number of components and members that can increase weight of the engine itself, the cylinder head member preferably is slim, simple and compact.
The engine also is provided with an air induction system to introduce air to the combustion chambers. Intake components such as, for example, a plenum chamber, can depend from the cylinder head member as well as the exhaust manifold. The air induction system also includes one or more intake valves and a valve actuation mechanism that are configured similarly to the exhaust valves and the valve actuation mechanism for the exhaust valves. Guide openings for intake valve lifters also provided in the air induction system, accordingly. It has also been discovered the that weight of the intake components can deform the guide openings for the lifters of the intake valves.
A further need therefore exists for an improved four-cycle engine that can prevent guide openings for valve lifters of either the exhaust or intake valves from deforming even though either exhaust or intake components depend from the cylinder head member.
In accordance with yet another aspect of the present invention, a four-cycle internal combustion engine comprises a cylinder block defining a cylinder bore. A piston is reciprocally disposed within the cylinder bore. A cylinder head member closes an end of the cylinder bore to define a combustion chamber together with the cylinder bore and the piston. The cylinder head member defines an inner passage having a first end communicating with the combustion chamber and a second end terminating at an outer surface of the cylinder head. A valve assembly having a valve section and an actuateable section is provided. The valve section is selectively placed at an open position and a closed position to connect and disconnect the inner passage with the combustion chamber, respectively. The actuateable section is formed oppositely from the valve section. A valve actuation mechanism is arranged to actuate the actuateable section to move the valve section between the open position and the closed position. The cylinder head member further defines a guide opening through which the actuateable section is slideably disposed. An external conduit defines an outer passage communicating with the inner passage. The external conduit depends from an end portion of the cylinder head member. The cylinder head member still further defines a recessed portion between the guide opening and the second end of the inner passage.
In accordance with another aspect of the present invention, an engine includes an engine body. The engine body includes a guide opening and a member slidably mounted within the guide opening. A mounting boss is disposed on an outer surface of the engine body. A recess disposed between the guide opening and the mounting boss.